When I was thirteen, my family went to the pageant in Palmyra, western New York state. We parked among many cars and buses. The rolling hills and fields were green, and the sky was heavy with dark clouds. I could hear other Mormons all around us in the crowd talking about how it wouldn't rain, because the Lord had never let it rain on the pageant. This hill we gathered beside was the real Hill Cumorah. Great battles had been fought here in Book of Mormon times. The pageant was to celebrate the truth of the BoM. Toward nightfall a steady drizzle began to fall from the dark skies. No one could admit that it was raining, so everyone's hair was uncovered and soaked. Water streamed over their denying faces. No rain, as it just couldn't be.
By this time I was already aware of the sham of Mormonism. All I had to do was look around to see it with my own eyes. I had never seen people get so damp when it wasn't raining, and I found that more amusing than the boring Nephite play on the hill. Happy Mormons squinted through the light rain and watched fake history being re-enacted in a blessed stupor. To them, the precipitation was fake and the shit show was real.
I grew up near Palmyra, and afternoon thunderstorms generated by the heat of the day were quite common. Often it would rain hard late in the afternoon, and then stop as suddenly as it started, which is pretty much par for the course for heat generated thunderstorms. That is probably where this faith promoting rumor came from.
Sometimes the rain didn't stop inn time for the start of the show. Or sometimes it started during the show. Rain of some sort was pretty much an annual event. The Hill Cumorah Pageant helped launch my cynicism about Mormonism's faith-promoting myths.